1849.] 



exercised hy Trees on Clhnale. 



441 



The house in which we resided in Fife was built on a greenstone 

 rock on the south brow of the liigh ground overlooking the beautiful 

 river Leven, about two hundred feet above its level, and five hundred 

 feet distant from it. We there remarked that, even in closets in the 

 garrets, shoes and all kinds of leather, soon become mouldy, which could 

 be produced only hy the moisture generated by the trees, which in thick 

 groves closely surrounded the house.* 



Trees in full foliage have long been noted as great attractors of 

 humidity and a young wych elm in full leaf affords a good example 

 of this supposed power ; but in the winter of the year when trees 

 are perfectly denuded thil faculty of creating moisture about them is 

 equally obvious though not so profusely. A strongly marked instance 

 of this was witnessed by me, when ascending a hill in the month of 

 March. The weather had previously been very fine and dry, and 

 the road in a dusty state ; but a fog coming on an ash tree hanging 

 over the road was dripping with water so copiously, that the road 

 beneath was in a puddle, when the other parts continued dry and ma- 

 nifested no appearance of humidity. That leaves imbibe moisture by 

 one set of vessels and discharge them by another is well known, but 

 these imbibings are never discharged in falling drops : the real mys- 

 tery was the fog in its progress was impeded by the boughs of the 

 trees, and gradually collected on the exposed side of them, until it 

 became drops of water, whereas the surrounding country had only 

 a mist flying over it. Thus in fact the tree was no attractor, but a 

 condenser ; the gate of a field will in the same manner run down 

 with water on the one side, and be dry on the other, as will a stick 

 or a post, from the same cause. It is upon this principle that cur- 

 rents of air will be found under trees in summer, when little is per- 

 ceived in open places and the under leaves and sprays will be curled 

 and scorched at times, when the parts above are uninjured. The air 

 in its passage being stopped and condensed against the foliage of the 

 tree, it accordingly descends along its surface or front and escapes at 

 the bottom where there are no branches or leaves to interrupt its pro- 

 gress. In winter there is little to impede the breeze in its course, 

 and it passes through; consequently at this season the air under a 

 tree is scarcely more sensibly felt than in the adjoining field. f 



* White's Natural History of Selborne, p. 195. 

 t Journal of a Naturalist, p. 61. 



